The present invention relates to a product wrapping method for producing tubular wrappings.
In particular, the present invention relates to a method of wrapping parallelepiped products, such as packets or packs of cigarettes, to which the following description refers purely by way of example.
On cigarette wrapping, packing and cellophaning machines, a tubular wrapping is formed about the product by a wrapping device comprising a wrapping wheel conveyor having a number of equally-spaced peripheral radial seats for receiving a respective product for wrapping.
The above known wrapping device normally also comprises a loading station, and a drive device for rotating the wrapping wheel in steps about its axis in such a manner as to successively arrest the seats in the loading station where the product and respective wrapping element (sheet or blank) are loaded on to the wheel. More specifically, as each seat on the wrapping wheel is arrested at the loading station, the wrapping element is normally fed in front of the inlet opening in the seat, and the product inserted radially through the inlet opening, so as to draw the wrapping element inside the seat and fold it in a U about the product. Once the product is fully inserted inside the seat, the wrapping element presents two longitudinal portions projecting outwards of the seat, and which are subsequently folded and connected one on top of the other to complete said tubular wrapping.
On known wrapping devices of the aforementioned type, a first of the two projecting portions, the trailing or upstream one in relation to the rotation direction of the wrapping wheel, is folded first by means of a mobile external folding device fitted to the loading station and operated before the wrapping wheel is started up again; while the second projecting portion, the leading or downstream one in relation to the rotation direction of the wrapping wheel, is folded on top of the first by a fixed folding device located outwards of the wrapping wheel and which contacts the second portion as the wrapping wheel is started up again.
Said fixed folding device normally extends over a relatively wide arc about the edge of the wrapping wheel, for holding the second portion in position on top of the first pending stable connection of the second to the first portion either by gumming or, in the case of heat-sealable wrapping material, by sealing.
The above known wrapping method presents several drawbacks, mainly due to the presence of said fixed folding device. More specifically, as a consequence of said second portion, once folded down on top of the first, rubbing against the surface of the fixed folding device, this must be so positioned as to allow a certain amount of clearance between itself and the outer edge of the wrapping wheel, to prevent the second portion from being in any way damaged, which clearance, however, inevitably results in imperfect folding of the second portion and in relatively weak contact pressure between the overlapping first and second portions.
In the event, for example, of the two portions being gummed together, insufficient contact pressure may result in the second portion coming unstuck, so that the wrapped product is subsequently rejected.
In the case of heat-sealing, on the other hand, connection is normally impaired by the second portion having to be held in place by the fixed folding device during sealing.
That is, if, as is preferable, the two portions are sealed along the free edge of the second portion, the fixed folding device must normally present an opening extending over the central portion of the overlapping portion for enabling passage of the sealing device, operation of which is thus obviously limited to the length of the opening as opposed to the entire length of the overlapping portion.
Alternatively, the entire length of the overlapping portion may be sealed by arresting the wrapping wheel in such a position that the overlapping portion projects partially beyond the fixed folding device, with the free edge of the second portion held down by the end of the device. In this case, the overlapping portion is obviously sealed a given distance from the free edge of the second portion, the outer portion of which thus remains unsealed.